snubber capacitor help - halogen lights

[Eric]

I just bought 3 low voltage halogen pendant lights. Inside the canopy, each
light has a small transformer with 120VAC primary and a 12VAC secondary. The
lights cause a tremendous amount of interference on AM radio in the kitchen
and makes it so you can hardly listen to anything except the strongest
stations. I am no electronics expert, but I have some RIFA PMR 210 snubber
capacitors I was thinking of trying across the primary, secondary or both.
My knowledge is very limited and I have only used these capacitors in my job
to solve some problems across relay coils.
From looking around, this seems to be a "X" capacitor (line to line).
However, I noticed that the interference gets worse when the ground touches
the shield of the light cable which is connected to one side of the
secondary. So I am concerned I need a "Y" type (line to ground). Anyway, I
plan to try the capacitors that I have. Does anyone have experience with
this problem? Any suggestions on the type / value of capacitors I should be
using? Is there another way to solve the problem?
Thank you.

 

[Watson A.Name - \Watt Sun, the Dark Remover\]

I just bought 3 low voltage halogen pendant lights. Inside the canopy, each
light has a small transformer with 120VAC primary and a 12VAC secondary. The
lights cause a tremendous amount of interference on AM radio in the kitchen
and makes it so you can hardly listen to anything except the strongest
stations. I am no electronics expert, but I have some RIFA PMR 210 snubber
capacitors I was thinking of trying across the primary, secondary or both.
My knowledge is very limited and I have only used these capacitors in my job
to solve some problems across relay coils.
From looking around, this seems to be a "X" capacitor (line to line).
However, I noticed that the interference gets worse when the ground touches
the shield of the light cable which is connected to one side of the
secondary. So I am concerned I need a "Y" type (line to ground). Anyway, I
plan to try the capacitors that I have. Does anyone have experience with
this problem? Any suggestions on the type / value of capacitors I should be
using? Is there another way to solve the problem?
Thank you.

Any time one connects a capacitor from hot to ground, etc., the current
is supposed to be limited to a few mA, and the "y" cap size is usually
4.7 nF or less. This is for safety reasons.

 

[Stig Carlsson]

I just bought 3 low voltage halogen pendant lights. Inside the canopy, each
light has a small transformer with 120VAC primary and a 12VAC secondary. The
lights cause a tremendous amount of interference on AM radio in the kitchen
and makes it so you can hardly listen to anything except the strongest
stations. I am no electronics expert, but I have some RIFA PMR 210 snubber
capacitors I was thinking of trying across the primary, secondary or both.
My knowledge is very limited and I have only used these capacitors in my job
to solve some problems across relay coils.
From looking around, this seems to be a "X" capacitor (line to line).

What you have is not only a capacitor but a RC-unit with a resistance in
series with the capacitor, see
http://www.evox-rifa.com/n_america/film_capacitor_catalog.htm . The
resistance will of course increase the impedance so the attenuation at radio
frequencies will be less.

If you want just the capacitance a PME 271 from Evox-Rifa would be better.
An X-capacitor is ok as long as you do not connect it to earth, for that you
will need a Y-capacitor.

For technical information see this page:
http://www.evox-rifa.com/n_america/technotes_filmcaps.htm

Regards
Stig Carlsson

 

[Eric]

Thanks. It looks like I should use .47uf capacitors because they seem to
attenuate the AM radio frequency range the best according to the Rifa
charts. Do you agree?
Any idea where to buy them retail? The local electronics shops in NJ never
heard of X and Y capacitors and Rifa's distributors only sell wholesale.
Please let me know if you have any ideas.
Thanks.

 

[Graham W]

Eric,

It occurs to me that the PSU you have there is not a simple transformer
but a switched mode power supply (SMPS). Therefore radio
interference from it may well indicate a faulty unit and in any case,
in these days is most likely to be outside of legislated emission limits.

You could perhaps use a real copper/iron transformer to eliminate
the problem.

 

[Stig Carlsson]

Thanks. It looks like I should use .47uf capacitors because they seem to
attenuate the AM radio frequency range the best according to the Rifa
charts. Do you agree?
Any idea where to buy them retail? The local electronics shops in NJ never
heard of X and Y capacitors and Rifa's distributors only sell wholesale.
Please let me know if you have any ideas.
Thanks.

Sorry, I live in Sweden so I can not help you where to get the capacitors.
Anyway the brand of capacitor is not important, any X-capacitor with enough
voltage rating will be ok to try. If the shop staff do not know X- and
Y-capacitors maybe they are more familiar with the term interference
suppressors. A local tv repair shop (if they exist anymore) should be able
to supply you with some, new or used.

Stig Carlsson